This invention relates to method an apparatus for controlling apparatus and in general to such apparatus or method in which the magnitude of the drive signal to the apparatus under control is calculated. More specifically, the method and apparatus is based on the known sliding mode control technique which involves predefining the dynamic response of the output of the apparatus under control by describing the paths that output is to follow on a phase plane of the output. The phase plane is a two or more dimensional plane having as its axis the controlled states. The control action is determined by the position on the phase plane of the actual output compared with the path describing the desired trajectory or hyperplane. Consequently, sliding mode control is dependent on the measurement of the output of the apparatus under control and its derivatives and the calculation of the actual position of the output at a given instant on the phase plane. For sliding mode control, the number of derivatives required by the control system equals the predominant order of the apparatus under control.